This invention relates to thin-film photovoltaic materials and manufacturing methods. More particularly, the invention provides a method for the manufacture of thin-film photovoltaic absorber materials which include sodium doping in the formation of a CIGS/CIGSS-based absorber material.
From the beginning of time, mankind has been challenged to find ways of harnessing energy. Energy comes in the forms such as petrochemical, hydroelectric, nuclear, wind, biomass, solar, wood and coal. Over the past century, modern civilization has relied upon petrochemical energy as an important energy source. Petrochemical energy includes gas and oil. Unfortunately, the supply of petrochemical fuel is limited and essentially fixed based upon the amount available on the planet Earth. Additionally, as more people use petroleum products in growing amounts, it is rapidly becoming a scarce resource.
More recently, environmentally clean and renewable sources of energy have been desired. One type of clean energy is solar energy. Solar energy technology generally converts electromagnetic radiation from the sun to other forms of energy. These other forms of energy include thermal energy and electrical power. For electrical power applications, solar cells are often used. Although solar energy is environmentally clean and has been successful to a point, many limitations remain to be resolved before it becomes widely used. As an example, one type of solar cell uses crystalline materials, which are derived from semiconductor material ingots. These crystalline materials can be used to fabricate optoelectronic devices that include photovoltaic and photodiode devices that convert electromagnetic radiation into electrical power. However, crystalline materials are often costly and difficult to make on a large scale. Additionally, devices made from such crystalline materials often have low energy conversion efficiencies.
Other types of solar cells use “thin film” technology to form a thin film of photosensitive material to be used to convert electromagnetic radiation into electrical power. Similar limitations exist with the use of thin film technology in making solar cells. That is, efficiencies for thin-film photovoltaic cells based on various types of absorber materials are often relative low. Additionally, some film ingredients such as sodium were found to be helpful for enhancing grain formation of copper based photovoltaic absorber material, but also found harmful of the integration of electrode materials associated with the device, especially for large scale manufacture. How to incorporate the right doping ingredient into thin films with desired concentrations is still largely undeveloped.